1. Field of the Invention
The present invention relates to a form-fill-seal packaging machine for forming a band-like film into packaging bags and sealing products into the packaging bags in sequence.
2. Description of the Related Art
Generally, a form-fill-seal packaging machine which forms a band-like film into packaging bags and seals products into the bags in sequence is constructed as disclosed in Japanese Unexamined Patent Publication No. H3-1362. The band-like film played out from a roll is formed into a tube with the side edges thereof held overlapped while the film is transferred along a transfer route. The overlapped side edges of the tubular film are bonded (lap, fin or pinch sealed for example). The lower end of the tubular film is sealed laterally. The products are supplied into the tubular film, and then the upper end of the tubular film is laterally sealed to separate the sealed tubular film from the remaining portion so that packaging bags each having the product sealed therein are produced in sequence.
In the above case, the sealing of the tubular film in the lateral direction is generally performed by heating and pressure-bonding the tubular film by bringing a pair of devices called sealing jaws arranged across the film transfer route into contact with each other. In this case, however, the method of bringing the sealing jaws into contact with each other by reciprocating the jaws in directions in which they come in contact with, and separate from, each other has the disadvantage that since the sealing of the film can be made only at the point of contact between the pair of sealing jaws, the transfer of the film has to be stopped for a time required for sealing. To avoid such a disadvantage, there has conventionally been known a method in which the sealing jaws are reciprocated in directions in which they come into contact with, and move away from, each other and also reciprocate along the film transfer route and when the sealing jaws are held in contact with each other, they are moved in the film transfer direction while they are held in the same condition. They thereby follow the tubular film so that the tubular film is laterally sealed as it is continuously transferred.
However, the conventional form-fill-seal packaging machine causing such sealing jaws to make such a motion has had the disadvantage costs are increased since two drive sources are required, one to drive the sealing jaws in which they reciprocate toward and away from each other and a second drive source to move the sealing jaws along the film transfer route. Especially, where the sealing jaws are reciprocated along the film transfer route by the second drive source, since the first drive source is also reciprocated, the inertia of the reciprocating motions becomes too large to increase the operating velocity of the machine and the second drive source is required to be an expensive large power type resulting in further increases in the manufacturing cost.